Mr. Rodrigues approaches Sérgio's compulsion with cold, behaviorist curiosity. The story traces the erosion of his humanity as he is pulled down into the garbage that surrounds him. But though his fate is shocking -- and detailed with a prurient moralism disguised as clinical detachment -- it is neither touching nor especially disturbing, since Sérgio is all but emotionless. He is, from the start, pointedly viewed as an animal who responds to others with either cruelty or desire, and so his descent into crime and then into a state of overt animality is neither surprising nor interesting.

He is clearly looking for danger and intensity, wrapping a shower cord around his neck to amplify the sensation as he masturbates, wearing handcuffs and a latex cat suit during sex, molesting a police officer. But both Mr. Meneses and the director emphasize Sérgio's affectlessness, making the movie both grueling and dull. Imagine (if possible) a Pasolini film without passion or politics, or an Almodóvar movie without beauty or humor, and you have some idea of the glum, numb experience of watching ''O Fantasma.'' Mr. Rodrigues may be fascinated by perversity, but he seems utterly indifferent to pleasure.

O FANTASMA

Directed by João Pedro Rodrigues; written (in Portuguese, with English subtitles) by Mr. Rodrigues, José Neves, Paulo Rebelo and Alexandre Melo; director of photography, Rui Poças; edited by Mr. Rebelo and Mr. Rodrigues; produced by Amândio Coroado; released by Picture This! Entertainment. At the Quad Cinema, 34 West 13th Street, Greenwich Village. Running time: 90 minutes. This film is not rated.